CN101671070B - Electric deionizing method and device containing protective water flow - Google Patents

Abstract

The invention relates to an electrodeionization method and device with protective water flow, which belongs to desalination and waste water treatment technology. Through the design of the three-compartment basic working unit, a protection chamber is set in the membrane stack, and a protective water flow is introduced into it, so that the electrodeionization device can avoid the metal in the membrane stack under the conditions of high hardness raw water and high concentration of heavy metal ion raw water. Hydroxide scale formation, safe and stable operation. The basic working unit of the membrane stack includes a desalination chamber, a concentrating chamber and a protection chamber arranged in sequence, and several basic working units are arranged repeatedly to form a membrane stack. The concentration chamber is filled with mixed-bed resin with excess anion resin, and the protection chamber is filled with resin in layers. The flow direction of concentrated water, desalinated water and protection water is opposite, and the protection water flow does not contain metal cations that can cause scaling. In this electrodeionization membrane stack, metal cations that can cause fouling cannot combine with OH ^- ions inside the membrane stack. The electrodeionization method and device can greatly reduce the investment and operating costs of a water treatment system, can efficiently recover valuable metals from industrial wastewater, and have important application values in pure water preparation and heavy metal wastewater treatment.

Description

Electrodeionization method and device including protective water flow

technical field

The invention relates to a method and device for desalination and waste water treatment, in particular to an electrodeionization method and device with protection water flow.

Background technique

Electrodeionization (EDI for short) is a water treatment technology that is filled with ion exchange resin in the desalination chamber between the ion exchange membranes of the electrodialyzer and organically combines electrodialysis and ion exchange. The core part of the EDI device is the membrane stack, which is generally composed of alternately arranged anion and cation exchange membranes, and filled with ion exchange resin between the membranes to form alternately arranged desalination chambers and concentration chambers. The water dissociation effect in the desalination chamber during the operation of EDI can dissociate water molecules into H ⁺ and OH ^- ions, so as to directly regenerate the filled part of the resin, so that continuous desalination and resin continuous can be realized at the same time Regeneration, completely eliminating the need to frequently regenerate ion exchange resins with chemical acids and bases. EDI is generally combined with reverse osmosis (referred to as RO) and other membrane separation processes to form an integrated membrane process. RO is placed upstream of EDI to remove organic impurities and about 98% of inorganic ions in advance, and EDI is obtained as a downstream deep desalination method. High resistivity pure water. Because of its remarkable advantages such as high efficiency, energy saving, and environmental friendliness, it has been widely used in the field of ultrapure water preparation in recent years.

However, the existing EDI technology has extremely strict requirements on the feed water conditions. The core problem is that when the feed water hardness is too high, metal hydroxide scaling deposits are easily formed inside the membrane stack, resulting in irreversible destructive Influence. This scaling is generally due to the combination of Ca ²⁺ , Mg ²⁺ hardness ions in the feed water with OH ^- ions, one of the water dissociation reaction products in the desalination chamber. In order to prevent scaling, EDI requires that the hardness of the incoming water should not exceed 1mg·L ^-1 , and many commodity EDIs even require that the hardness of the incoming water should not exceed 0.5mg·L ^-1 . Such strict influent conditions also impose strict requirements on the RO process upstream of EDI. In most cases, two-stage RO is required as EDI pretreatment. In terms of the same water yield, the investment of a water treatment system using two-stage RO is 2-3 times that of one-stage RO, and the amount of RO concentrated water discharged is more than twice that of one-stage RO, which significantly increases investment costs and operating costs , It also limits the wider application of EDI water treatment technology to a certain extent. Therefore, it is of great significance to relax the restriction on influent conditions by developing new EDI technology, so that in more cases, only one-stage RO can be used as pretreatment to meet the requirements.

In the existing EDI technology, there are mainly two methods for scaling prevention and control. One is to add scale inhibitors to the EDI influent, and the other is to adjust the pH value of the water flow, that is, to prevent scaling by adding acid. , or chemically clean the compartment of the EDI with acid after scaling has formed. These two methods additionally increase the desalination burden of EDI, which is not conducive to obtaining high-quality pure water; additional chemicals entering the membrane stack will also reduce the current efficiency and operating efficiency of EDI, increase process energy consumption, and easily form secondary secondary pollution.

In addition to pure water preparation, EDI and some improved EDI technologies have also begun to be tried for wastewater treatment containing heavy metal ions. Compared with pure water preparation, not only the influent concentration of the treated raw water is greatly increased, but also heavy metal ions like Cu ²⁺ , Ni ²⁺ , Pb ²⁺ etc. are more likely to form scale deposits with OH ^- ions. Therefore, the problem of heavy metal hydroxide scaling prevention has become the core problem to be solved in this research and application direction.

Contents of the invention

The purpose of the present invention is to provide a novel EDI water treatment method and device that can effectively solve the scaling and precipitation of metal hydroxides in the EDI membrane stack in view of the above problems and the shortcomings of the existing EDI water treatment technology. The present invention sets a protection chamber in a conventional EDI membrane stack, introduces a protection water flow into it, and adopts a special filling strategy and water flow operation process, so that Ga ²⁺ , Mg ²⁺ hardness ions and heavy metal ions that may cause scaling cannot be mixed with OH ^- ions are combined inside the membrane stack, thus avoiding scale formation. This new EDI water treatment process can not only stably produce ultrapure water with a resistivity of 17MΩ·cm when the hardness of the influent water reaches 10mg·L ^-1 , but also can target heavy metals such as Ni ²⁺ and Cu ²⁺ The industrial wastewater with ions of hundreds of mg·L ^-1 is efficiently separated and treated, the process operation is more stable, and the life of the EDI membrane stack is significantly extended.

The present invention is achieved through the following technical solutions:

Positive and negative electrode chambers and corresponding polar water protection chambers are respectively arranged on both sides of the EDI membrane stack, and the electrode chamber and the polar water protection chamber are separated by a cation exchange membrane. Between the extreme water protection chambers are the basic working units of the membrane stack arranged in a certain number of repetitions. Unlike traditional electrodialysis (ED) and EDI technologies, where each basic working unit includes a desalination chamber and a concentrating chamber, each basic working unit of the EDI membrane stack in the present invention changes from the direction of the positive pole to the direction of the negative pole. It includes three compartments in total, that is, "desalination chamber-concentration chamber-protection chamber", which are arranged in sequence. Several of these three-compartment basic working units are arranged repeatedly to form a membrane stack. In the three-compartment basic working unit, the concentration chamber and the protection chamber are separated by an anion exchange membrane, the desalination chamber and the concentration chamber are uniformly filled with mixed-bed resin, and the protection chamber is filled with resin in layers. Most of the resin bed along the water inlet to the water outlet of the protection chamber is filled with anion exchange resin; while a small amount of resin bed near the water outlet in the protection chamber is filled with mixed bed ion exchange resin. Driven by the DC electric field, the cations in the water flow in the desalination chamber pass through the cation exchange membrane and migrate into the adjacent concentrating chamber; the anions migrate through the anion exchange membrane into the adjacent protection chamber. In each basic working unit, the flow direction of the desalinated water and the protection water are the same, and the flow direction of the concentrated water flow between the two water flows is opposite to it. The protection water flow does not contain any OH ^- ions that can be combined to generate Cationic for metal hydroxide scaling. Furthermore, both the protection water and the concentrated water are operated in a partial circulation process. A small amount of effluent of the protection water enters the concentrated water circulation system, while the desalinated product water has an equal flow of water flow into the protection water circulation system for replenishment; for the concentrated water circulation system, the same flow of water flows out as concentrated product water.

According to the above-mentioned water flow operation process, no additional third-party water flow is required as protection water during operation. The protection water flow is obtained from a very small amount of desalinated effluent, and circulates in the whole system. Except for the polar water system, the entire EDI operating system has only one feed water flow and two product water flows, namely desalinated raw water, desalinated product water and concentrated product water. The sum of the flow of the latter two is equal to the flow of desalinated raw water. The flows of these three water streams can be adjusted arbitrarily according to needs, so the operation flexibility is large and the maneuverability is strong.

The above-mentioned electrodeionization method and device with protective water flow have the following characteristics:

1. In each basic working unit of the membrane stack, from the positive electrode side to the negative electrode side, there are three compartments in sequence: the desalination chamber, the concentration chamber and the protection chamber. The desalination chamber and the concentration chamber are separated by a cation exchange membrane. The concentration chamber and the The protection chambers are separated by anion exchange membranes;

2. The desalination chamber, concentration chamber and protection chamber are filled with ion exchange resin according to different filling strategies. The desalination chamber and concentration chamber are filled with uniform mixed bed resin, and the concentration chamber is filled with anion exchange resin. The volume ratio is 55-95%; the resin bed in the protection chamber is divided into upper and lower parts, and the resin bed near the water inlet accounts for 50-85% of the total resin bed volume, and the filled resin is anion exchange resin , and the resin bed near the water outlet accounts for 15-50% of the total resin bed volume, and the filled resin is an anion-yang mixed bed resin;

3. In each three-compartment basic working unit, the flow direction of desalinated water and protection water is the same, and the flow direction of concentrated water is opposite;

4. Concentrated water and protected water adopt partial circulation process to operate. A small amount of water flow from the desalinated product water is used as supplementary water for protection water, a small amount of water flow from the protection water is used as supplementary water for concentrated water, and a small amount of water flow from the concentrated water circulation tank is concentrated product water, and the flow rates of the three streams are equal to concentrate The water volume in the water circulation tank and the protection water circulation tank is kept constant during operation.

In the present invention, the concentration chamber is filled with mixed-bed resin with anion resin volume ratio of 55-95%. On the one hand, filling the concentrating chamber with resin requires the use of a compartment of increased thickness compared to a thin compartment that is not filled with resin. This makes the migration path of metal cations in the direction parallel to the electric field increase significantly; Water flows out of the module. Both of these factors significantly reduce the probability of metal cations combining with anions, including ^OH- ions, which is beneficial to prevent the formation of scale in the concentration chamber. In addition, although the thickness of the concentrating chamber is larger than that of the thin compartment, the electrical conductivity of the filled resin is much higher than that of the concentrated water flow, which makes the resistance of the concentrating chamber filled with resin not high under certain conditions. The electrical resistance of the thin concentrating chamber, which is not filled with resin, is even lowered without increasing the power consumption of the process.

In the present invention, the resin bed in the protection chamber is divided into upper and lower parts, wherein the resin bed near the water inlet accounts for 50-85% of the total resin bed volume, and the filled resins are all anion exchange resins. This can promote the salt anions in the desalination chamber in the next basic working unit adjacent to the protection chamber, and further migrate into the concentration chamber after entering the protection chamber, so as to realize the complete concentration of cations and anions; while the resin bed near the water outlet It accounts for 15-50% of the total resin bed volume, and the filled resin is a mixed bed resin of yin and yang. The cation resin in this part of the resin bed can specifically suppress the product OH ^- ions of the intense water dissociation reaction on the surface of the anion exchange membrane near the water outlet in the desalination chamber in the next basic working unit adjacent to the protection chamber, After entering the protection chamber, it continues to migrate towards the positive electrode and enters the concentration chamber. This is because, for the EDI process, water dissociation always occurs violently on the surface of the ion exchange membrane and resin particles near the outlet of the desalination chamber; while at the water inlet near the desalination chamber, due to the anion and cation content in the water flow is not yet high Very low, the degree of water dissociation is relatively weak.

Further, according to the present invention, the flow direction of concentrated water in the EDI membrane stack is opposite to the flow direction of protection water and fresh water. This makes it possible that in each concentration chamber, the metal cations migrating into the desalination chamber will be taken out of the membrane stack by the concentrated water flow at the fastest speed, and the accumulation of metal cations will not occur in the concentration chamber; in addition, the desalination chamber is close to the water outlet. One of the products of water dissociation on the surface of the anion exchange membrane, ^OH- ions, will migrate towards the positive electrode. In this direction, there is a protection chamber between the desalination chamber and the concentration chamber to separate them. The OH ^- ions entering the protection chamber will be quickly taken out of the membrane stack by the protection water flow in the same direction and will not be difficult to enter the concentration chamber in front. Therefore, in each basic working unit, the highest concentration of metal cations and the highest concentration of ^OH- ions are not only in different compartments (concentration compartment and protection compartment) respectively, but also their water flow directions are opposite. In addition, when water dissociation occurs on the surface of the cation exchange membrane in the desalination chamber, one of its products, H ⁺ ions, will directly enter the concentrating chamber adjacent to it, and gradually accumulate in the concentrating chamber along with the concentrated water flow, together with metal cations is taken out of the membrane stack. This makes the site with the highest concentration of metal cations also the site with the highest concentration of H ⁺ ions. Since the degree of water dissociation on the surface of the anion and cation exchange membranes in the EDI desalination chamber is equal in steady state, or the degree of water dissociation on the surface of the anion membrane is slightly weaker, even a small amount of OH ^- ions continue to migrate forward after entering the protection chamber Entering the concentrating chamber, its quantity is also far from enough to neutralize the continuously accumulating H ⁺ ions in the concentrating chamber. This ensures that the pH of the concentrated water stream will be maintained at a stable weak acidity, thereby preventing scale formation. For the protection chamber, since the water flow entering the protection chamber does not contain any metal ions that may scale, scaling will also not occur.

Obviously, according to the above operation process, with the operation of the EDI system, the pH value in the protection water circulation tank will gradually increase, while the pH in the concentrated water circulation tank will continue to decrease. Since the whole system operates without adding any other chemicals, the solutions in the two circulating water tanks can be properly neutralized and mixed into fresh water after a certain period of operation. After that, injecting fresh protection water can restore the system operation without affecting the recycling of concentrated water. Since the circulating liquid volume of the protection water and the concentrated water can be manually controlled manually, and the water volume can be large or small, so its influence on the fluctuation of the raw fresh water quality can also be controlled within a predetermined range.

According to the above-mentioned electrodeionization method with protective water flow, the electrodeionization device for realizing the method is realized through the following technical scheme. The electrodeionization device includes four parts: a membrane stack, an electrode device, a clamping support device and a clamping device. The clamping device is composed of two clamping plates, tension bolts and nuts; inside the two clamping plates are positive and negative electrode devices composed of positive and negative electrode chambers and electrode plates; according to the specific water quality of the treated raw water, it can also be In the inner side of the positive and negative electrode chambers, the electrode chamber protection chambers are respectively set; between the positive and negative electrode chambers is a clamping support device composed of a certain number of rectangular hollow support frame plates; in the hollow cavity of the hollow support frame plate is Membrane stack. The basic unit of the membrane stack consists of an anion exchange membrane, a desalination chamber partition, a cation exchange membrane, a concentration chamber partition, an anion exchange membrane, and a protection chamber partition. And fill the mixed bed resin in the desalination chamber, fill the mixed bed resin with anion resin volume ratio of 55-95% in the concentration chamber, and fill the layered resin in the protection chamber. The membrane stack can be assembled into a one-stage or one-stage multi-stage configuration as required.

The electrodeionization method and device containing protective water flow according to the present invention have the advantages of:

(1) EDI membrane stack structure based on the three-compartment basic working unit of "desalination chamber-concentration chamber-protection chamber", as well as different resin filling strategies in each compartment, reverse flow between concentrated water, desalinated water, and protected water The water flow operation method eliminates the possible metal hydroxide scaling and precipitation in the membrane stack, thus significantly relaxing the water inlet conditions of EDI and broadening the application range of this water treatment technology;

(2) For the three streams of desalinated water, concentrated water and protected water, the entire EDI system only needs one stream of fresh water to enter, and at the same time only two streams of desalinated product water and concentrated product water to exit, the system operation is more convenient;

(3) During the operation of the EDI membrane stack, there is no need to use scale inhibitors, and no chemical cleaning is required, which saves operating costs and produces no secondary pollution;

(4) Using the EDI method and device provided by the present invention for pure water preparation can reduce the upstream two-stage RO system to a one-stage RO system, thereby reducing the investment of the entire water treatment system and the discharge of RO concentrated water by 40% above;

(5) Applying the EDI method and device provided by the present invention to the treatment of heavy metal wastewater can realize simultaneous purification and concentration of wastewater under efficient, stable and clean conditions, which is conducive to the simultaneous recovery of pure water resources and valuable metals.

Description of drawings

Fig. 1 is a schematic diagram of the internal structure of the electrodeionization method containing the protective water flow provided by the present invention, and the number of the basic working units of the membrane stack shown in the figure is 2;

2 is a schematic diagram of the ion migration principle of the basic working unit in the internal structure of electrodeionization described in FIG. 1 (taking _NiSO solution as an example);

3 is a schematic cross-sectional view of an electrodeionization device containing a protective water flow provided by the present invention,

Fig. 4 is a cross-sectional exploded schematic view of the electrodeionization device containing the protective water flow described in Fig. 3, wherein only one hollow supporting frame plate is shown;

Fig. 5 is the specific flowchart of a kind of embodiment device provided by the present invention;

In the picture above:

1-cation exchange membrane; 2-anion exchange membrane; 3-basic working unit; 4-cation exchange resin; 5-anion exchange resin; 6-positive chamber; 7-negative chamber; 8-positive protection chamber; 9-negative protection 10-desalination chamber; 11-concentration chamber; 12-protection chamber; 13-fresh water inlet; 14-concentrated water inlet; 15-protection water inlet; 16-positive water inlet; 17-positive water outlet; Negative electrode water inlet; 19-negative electrode water outlet; 20-desalination water production; 21-desalination product water distribution; 22-concentrated water circulation water; 23-concentrated product water; 24-protection water circulation water; 25-protection water distribution; 26-positive side Clamping plate; 27- negative side clamping plate; 28- positive electrode plate; 29- negative electrode plate; 30- hollow support frame plate; 31- tension bolt; 32- nut; Valve; 35-fresh water pump; 36-concentrated water circulation pump; 37-polar water pump; 38-protection water pump; 39-pressure gauge; 40-rotameter; 41-concentrated water circulation tank; 42-protection water circulation tank; 43-polar water circulation tank; 44-concentrated product water tank; 45-fresh water product water collection tank; 46-electrodeionization device

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, a cation exchange membrane and corresponding water flow partitions are respectively arranged behind the positive and negative electrode chambers on both sides of the membrane stack to form the pole water protection chamber of the membrane stack. The setting of the positive electrode protection chamber 8 can better prevent the harmful gas of the positive electrode reaction from oxidizing ^and destroying the first anion exchange membrane; the setting of the negative electrode protection chamber 9 can avoid the reduction of cations on the cathode and prevent the OH- produced by the negative electrode reaction Move to the protection room.

The positive electrode water 16 enters the positive electrode chamber 6 and the positive electrode protection chamber 8 through the lower part of the positive electrode side, and the positive electrode effluent 17 enters the negative electrode chamber 7 and the negative electrode protection chamber 9 through the external pipeline of the membrane stack as the negative electrode water inlet 18 after being exported from the upper part. The upper part of the negative electrode is exported into the electrode water circulation tank, and recycled after the gas generated by the electrode reaction is eliminated. The flow direction of the electrode water in the electrode chamber and the electrode water protection chamber is from bottom to top, which is conducive to the timely discharge of the gas generated by the electrode reaction from the EDI membrane stack. In addition, the water flows from the positive electrode to the negative electrode, so that the acidic positive electrode effluent enters the negative electrode chamber and neutralizes the OH ^- ions generated by the negative electrode reaction to eliminate the scaling of the negative electrode chamber.

According to FIG. 1 and FIG. 2 , each basic working unit 3 of a membrane stack includes a desalination chamber 10 , a concentration chamber 11 and a protection chamber 12 . The anions in the fresh water chamber 10, such as SO ₄ ²⁻ , are driven by the electric field to migrate through the anion exchange membrane 2 to the protection chamber 12 adjacent to the left. The desalinated water flow and the protection water flow are in the same direction, and the resin filled in the lower part of the protection chamber is an anion exchange resin, which can enhance the transfer of anions and make them continue to enter the concentration chamber 11 to be concentrated. At the fresh water outlet, the OH ^- ions produced by the water dissociation of the anion exchange membrane directly enter the protection chamber, that is, the protected water flow is quickly taken out of the EDI membrane stack; and because the resin filled in the upper part of the protection chamber is a mixed bed resin, this makes the OH ^- ions unable to Continue into the concentration chamber 10. For the desalination chamber 10, the H ⁺ ions produced by the water dissociation of the cation exchange membrane near the water outlet directly enter the concentrating chamber 10, and accumulate in the concentrating chamber along with the concentrated water flow until they are discharged from the membrane stack. This makes the entire concentrated water flow acidic from the inlet to the outlet, and the acidity is gradually strengthened, avoiding the formation of scale in the concentrated water chamber. The heavy metal ions entering the fresh water chamber, such as Ni ²⁺ ions, migrate into the concentration chamber on the right side under the action of the DC electric field, and are immediately taken out of the membrane stack by the concentrated water flow in the opposite direction. Therefore, no accumulation of heavy metal cations is formed in the concentrating compartment. Under the process conditions of concentrated water circulation, the concentration of heavy metal cations in the entire concentration chamber is relatively balanced.

In the mixed bed resin filled in the concentrating chamber 11, the volume ratio of the anion resin is greater than 50%. This makes the heavy metal Ni ²⁺ ions migrating in from the left desalination chamber 10 further hindered by more anion resins and cannot enter the protection chamber 12 . In addition, the protection water stream does not contain any scale-forming metal cations, so no scaling will occur in the protection chamber.

According to the process provided in FIG. 5 , raw fresh water enters the EDI device 46 from the fresh water tank 33 through the fresh water pump 35 , most of the effluent is collected into the fresh water production tank 45 , and a very small amount is diverted to the protection water circulation tank 42 . Concentrated water inflow enters the EDI device 46 from the concentrated water circulation tank 41 through the concentrated water circulation pump 36, most of the effluent returns to the concentrated water circulation tank 42, and a very small part is collected as product water to the concentrated product water tank 44. The protection water flows through the protection water circulation tank 42 and enters the EDI device 46 through the protection water pump 38 , most of the effluent returns to the protection water circulation tank 42 , and a very small amount of water flows into the concentrated water circulation tank 41 . The water flow of the desalinated product, the protected water flow, and the concentrated product are all equal, and the flow is controlled by the corresponding stop valve 34 and the rotameter 40 . During operation, the liquid levels in the concentrated water circulation tank 41 and the protection water circulation tank 42 are kept constant.

Example 1

In this example, the EDI device has a one-stage and one-stage structure, including two basic working units. Its cross-section is shown in Figures 3 and 4, and is used to treat NiSO ₄ wastewater containing heavy metal Ni ²⁺ ions with a concentration of 50 mg·L ^-1 . Concentrated, fresh water chamber and protective chamber partition specifications are 100*300*4mm, polar water partition specification is 100*300*0.9mm, effective membrane area is 160cm ² . The ion-exchange membrane used is a special-purpose ion-exchange membrane for heterogeneous low-permeability EDI, produced by Zhejiang Qianqiu Environmental Protection Water Treatment Co., Ltd.; the ion-exchange resins are D072 and D296 macroporous strong acid and strong basic resins. The volume ratio of anion and cation in the desalination chamber is 1:1; the volume ratio of anion and cation in the concentration chamber is 2:1; the lower 75% of the resin bed in the protection chamber is filled with anion resin, and the remaining 25% of the resin bed is filled with resin For mixed bed resins, the volume ratio of anion and cation resins is 1:2.

The raw fresh water tank 33 and the concentrated water circulation tank 41 are pre-configured with a 50 mg·L ⁻¹ NiSO ₄ solution with a pH of 4.25. Electrode water is a Na ₂ SO ₄ solution with a mass concentration of 0.3%. The flow rates of desalinated water, concentrated water and electrode water are 25L·h ^-1 , 15L·h ^-1 and 15L·h ^-1 respectively, and the flow rates of concentrated water production water, protection water diversion and fresh water diversion are all 0.36L·h ^-1 , The operating voltage of the membrane stack is 15V. The concentration of Ni ²⁺ in desalinated water and concentrated water was detected by flame atomic absorption spectrophotometry. The device operated stably for 24 hours, and the Ni ²⁺ concentration in the desalinated water quality was lower than 0.5 mg·L ^-1 , the rejection rate was 99%, while the Ni ²⁺ ion content in the concentrated product water finally reached 9000 mg·L ^-1 , The concentration factor reaches 180.

Example 2

In this embodiment, the EDI device adopts a one-stage two-stage structure, and each stage contains two basic working units for preparing high-purity water. The resins used are gel type 001×7 cation resin and 201×7 anion resin. Separator specification, ion exchange membrane etc. are all identical with embodiment 1,

Fresh water raw water tank 33, concentrated water circulation tank 41, and polar water tank 43 are pre-prepared with deionized water to add salt solution of CaCl ₂ and MgCl ₂ to prepare stock solution, wherein Ca ²⁺ ion concentration is 3 mg.L ^-1 and Mg ²⁺ ion concentration It is 1mg.L ^-1 , and the total hardness is 11.7mg.L ^-1 . The flow rate of desalinated water is 40L.h ^-1 , the flow rate of concentrated water, protection water and electrode water entering the EDI membrane stack is 6L.h ^-1 , and the flow rate of the three split streams is 1L·h ^-1 . The membrane stack operates at a constant voltage of 40V. After 320 hours of operation, the water resistivity of the desalinated product gradually increased to 15MΩ.cm within 15 hours after starting up, and remained between 16.5-17.0MΩ.cm for most of the time thereafter.

The examples show that by using the EDI method and device provided by the present invention containing the protective water flow, the EDI process can still be efficient under the condition that the cation concentration that is easy to form metal hydroxide scaling is much higher than the existing EDI influent index. , stable and safe operation. This new EDI water treatment technology has important application value in the fields of water desalination and purification and industrial wastewater treatment. It can greatly reduce the investment and operation costs of water treatment systems, and effectively recover valuable metals in wastewater.

Claims (4)

1. one kind contains the electric deionizing method of protecting current, by the protection chamber being set in the electrodeionization membrane stack and introducing the protection current therein and avoid in membrane stack, forming the metal hydroxides fouling, its membrane stack is made up of several groundwork unit, it is characterized in that in each groundwork unit, diluting compartment, three compartments in enriched chamber and protection chamber are arranged from the side of the positive electrode to the negative side successively, separate with cation-exchange membrane between diluting compartment and the enriched chamber, separate with anion-exchange membrane between enriched chamber and the protection chamber; Carry out resin by following strategy and fill in diluting compartment, enriched chamber and the protection chamber of membrane stack, promptly fill even mixed-bed resin in diluting compartment and enriched chamber, wherein the shared volume ratio of anion exchange resin is 55-95% in the enriched chamber; Resin bed is divided into two parts up and down in the protection chamber; wherein account for the 50-85% of total resin bed volume near the resin bed of water inlet; and institute's potting resin is anion exchange resin; and the resin bed of close delivery port accounts for the 15-50% of total resin bed volume, and institute's potting resin is the negative and positive mixed-bed resin.

2. the electric deionizing method of protecting current that contains according to claim 1; its feature is that also the operation process of condensed water and protection current is the part circulation; and protection water supplementing water is provided by desalination product moisture stream; the condensed water supplementing water is provided by protection water water outlet shunting; concentrated product water is got by the shunting of the condensed water circulatory system, and the discharge of this three stocks stream all equates.

3. the electric deionizing method of protecting current that contains according to claim 1, its feature are also in each membrane stack groundwork unit that desalination water is identical with the water (flow) direction of protection water, and opposite with the water (flow) direction of condensed water.

4. one kind contains the electric deionizer of protecting current, comprise membrane stack, electrode assembly, clamping bracing or strutting arrangement and clamping device four parts, wherein membrane stack is made of the groundwork unit of several repeated arrangement, it is characterized in that each groundwork unit has diluting compartment dividing plate, enriched chamber's dividing plate and protection chamber dividing plate totally three dividing plates successively from the side of the positive electrode to the negative side, separate with cation-exchange membrane between diluting compartment dividing plate and the enriched chamber's dividing plate, separate with anion-exchange membrane between enriched chamber's dividing plate and the protection chamber dividing plate; Carry out resin by following strategy and fill in diluting compartment, enriched chamber and the protection chamber of membrane stack, promptly fill even mixed-bed resin in diluting compartment and enriched chamber, wherein the shared volume ratio of anion exchange resin is 55-95% in the enriched chamber; Resin bed is divided into two parts up and down in the protection chamber; wherein account for the 50-85% of total resin bed volume near the resin bed of water inlet; and institute's potting resin is anion exchange resin; and the resin bed of close delivery port accounts for the 15-50% of total resin bed volume, and institute's potting resin is the negative and positive mixed-bed resin.

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